1. Field of the Invention
This invention relates to an optical recording medium which performs optically recording of information and its optical recording and reading system.
2. Related Background Art
In recent years, with the progress of information-oriented society, a large number of optical recording media and recording-reproducing devices of information have been proposed which perform recording, reproduction of optical information such as an optical disc, optical card, optical tape, etc. as the means for dealing with a diversity of information. In optical recording media, there has been known one in which the information formed into binary value can be detected by conversion into a change in reflectance or a change in intensity of the reflected light accompanied with the surface shape such as presence of a pit (concavity). Such optical recording medium is constituted of a preformat signal and a guide groove previously provided on a substrate according to the 2P method, compression molding, cast molding, etc., an amorphous thin film of a dye or pigment such as cyanine type or polymethine type, TeOx, chalcogen, etc. coated of vapor deposited thereon as the optical recording layer capable of recording and reproduction with light, and further a protective substrate for protection of the above optical recording layer laminated thereon, if desired.
Among such an optical recording media, optical card has dimensions of, for example, 85.4 mm.times.54.0 mm.times.0.76 mm and is excellent in portability. However, such an optical recording medium is liable to be flawed during carrying. Particularly, optical card, on account of its portability, is susceptible to formation of flaws, contamination, etc., whereby there ensue such problems that tracking is liable to cause slippage and that C/N ratio of the reproduced signal is lowered.
As the method for solving such problems, there have been proposed in the art an optical card which performs recording and reproduction with a protective sheet attached on the recording and reproducing light incident surface of an optical card, while peeling off the protective sheet corresponding to flaws and contamination as described in Japanese Patent Laid-open Application No. 60-120097 or prevention of flaws by providing a hard coat layer on the recording and reproducing light incident surface of the optical card. However, when the protective sheet is peeled off, there is the fear that the adhesive may be attached onto the surface of the optical card to negative affect recording and reproduction.
Also, when a tacky protective sheet is plastered, to maintain its tacky strength at a certain strength and to peel it off easily can be satisfied at the same time with difficulty, because both are antagonistic to each other.
Also, as for the hard coat layer, when a flaw is once presents which makes reproduction impossible, the information on the optical card can be completely reproduced with difficulty.